Combustion heater sheet metal heat exchanger



July 1, 1958 F. A. RYDER coHBusTToN HEATER sHEET METAL HEAT ExcHANGEE Filed oct. ze, 195s 2 sheets-sheet 1 July l, 1958 F. A. RYDER COMBUSTION HEATER SHEET METAL HEAT EXCHANGER Filed Oct. 26, 1953 2 Sheets-Sheet 2 United States Patent O COMBUSTION HEATER SHEET METAL HEAT EXCHANGER Frank A. Ryder, Indianapolis, Ind., assignor to Stewart- Warner Corporation, Chicago, lll., a corporation of Virginia Application October 26, 1953, Serial No. 388,096

2 Claims. (Cl. 126-109) The present invention relates to sheet metal heat exchangers used in combustion heaters. More particularly it relates to the sheet metal portion of a small combustion heater to which the burner is attached. The burner may be of any suitable type. Heaters of this general character are used for heating the air in'automotive vehicles, airplanes, or for like service in which fuel is burned so as to heat a stream of Ventilating air passed through and around the heater heat exchanger. The portion of such a heater with which this invention is particularly concerned is the sheet metal structure which provides the heat exchange surfaces, the combustion space and combustion gas passages, and the passages for Ventilating air. For an example of such a heater, see Patent No. 2,507,081, issued MayA 9, 1950, to George W. Allen and Vernon N. Tramontini, for Sheet Metal lnternal Combustion Heater.

The primary objective of the present invention is to provide the sheet metal heat exchange portion and combustion chamber space of a heater at low cost.

A further object is to provide an arrangement for manufacturing such a structure, in which the several elements thereof are readily formed by efficient conventional techniques and in which these elements are secured together in assembled relationship largely by seam welding or related resistance welding techniques.

Still another object of the present invention is to provide an article of the type mentioned above which requires only a minimum of arc or gas welding.

Yet another object is to provide a heater heat exchanger which can be fabricated from comparatively light gauge stainless steel or similar metals in an economical fashion.

Other objects andadvantages will become apparent from the following description of a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings, in which similar characters of refer ence refer to similar parts throughout the several views:

Fig. 1 is a side view of a` combustion heater sheet metal heat exchanger embodying the features of the present invention;

Fig. 2 is an end view thereof;

Fig. 3 is an exploded view taken from the same end as Fig. 2 illustrating the individual elements which make up the major portion of the heat exchanger with the exception of the enclosing sheet and the exhaust pipe;

Fig. 4 is an end view of the enclosing sheet and exhaust pipe which is assembled with the elements of Fig. 3 in forming the heat exchanger; and

Fig. 5 is a vertical transverse sectional view that may be considered as taken in the direction of thearrows substantially along the line 5-5 of Fig. l.

Combustion heaters, particularly comparatively small size liquid fuel burning heaters of the hot air type which are used in automotive vehicles and for a similar service, consist essentially of a burner, a fuel supply and control system therefor, some means forcirculating combustion and Ventilating air, a heat exchanger portion which, in many instances at least, comprises the most expensive main structural element of the heater and a generally cylindrical case which surrounds the heat exchanger and burner. A heat exchanger for such a heater typically provides a central space into which hot gases issue from the burner. This space is commonly referred to as the combustion space or combustion chamber. Gas passages are also provided from this central combustion space to an exhaust fitting which conventionally is connected to van exhaust pipe leading to the atmosphere. ln addition, the heater heat exchange structure provides passages for Ventilating air which are in heat exchange relation to the hot products of combustion and ordinarily the external surface of the heat exchanger also is heated and heats air which passes through the space between the heat ex changer and the enclosing case. A heater having these general characteristics is well illustrated and described in the before mentioned patent and in a sense, therefore, the heat exchanger forming the subject matter of the present invention may be considered as an improvement over the heat exchanger which forms a portion of the subject matter of that patent, primarily in that it can be manufactured at considerably lower cost.

By referring to Figs. l, 2, and 5 of the present invention it will be seen that the structure there shown comprises an oval (itis almost cylindrical but somewhat higher than it is wide) horizontal enveloping sheet or shell 10 having an exhaust fitting or spud 12 extending from the lower side thereof. A pair of generally C-shaped Ventilating air tubes 14 and lo extend lengthwise of the heat exchanger and are enclosed Within the enveloping sheet 10. These tubes are coextensive in length with the shell 10 and are spaced therefrom intermediate the ends thereof. A portion of the Ventilating air to be heated passes through the spaces 18 and 2i) enclosed within the walls of the tubes 14 and 16, while an additional portion is heated by passing in contact with the exterior surface of the shell l0. Both ends of the heat exchanger, with the exception of the tubes 14 and 16 are closed by members indicated generally at 22 and 24, one of which, 24, has a circular flanged opening 25 therethrough for mounting a heater burner not shown.

As is best seen in Fig. 3, the tubes 14 and 16 are identical, excepting that one is used in a position which is an end to end reversal of the other so that the tubes as used are reverse complements of each other. Only one therefore needs to be described. The tube 14 is formed from a single strip of sheet metal, the gauge and composition of the metal being determined largely by the service life to be expected from the heat exchanger and the temperature at which the metal will be expected to operate. The conformation of the tube 14 is such that there is a downwardly extending tab 30 which extends' the length of the tube 14, that is, the length of the heat exchanger. This tab is formed by bringing the two ends of the sheet together in face to face relationship and welding these ends together throughout the length of the tube, preferably by seam resistance Welding technique. lust above the tab 30 both surfaces of the sheet metal extend abruptly outwardly at and then are separated so that the inner portion 32 of the continuous sheet is formed to a concave contour and at the upper end thereof is joined by a bight 34 to the outer surface forming sheet 36 which is substantially parallel with the inner surface 32 so as toform a curved slot of approximately uniform Width.

In the embodiment illustrated it should be noted with respect to the tube 14 that the inner surface forming member 32 extends horizontally from the tab Sil for almost no distance at all before sweeping into the curved concave contour described above. On the other hand, the

outer ,surface forming sheet portion 36 extends straight horizontally from the tab 3i). for an appreciable distance, indicated at 38, before curving outwardly and upwardly.

This tube le and its reverse complement .161are then brought together with the tab Stl on the tube .14 and its counterpart on the tube 16 in face to-face relationship. With the tubes as thus arranged they are-run through a seam Welder .so as to weld the tabs S3iwand 44)..together throughout the full length of the tubes. The two'tubes together, therefore, form a generally VU-shaped article with the upper ends of the U curved inwardly toward each other somewhat and with atab-or rib consisting of four thicknesses of the metal'extending straight l.downwardly for a short distance from the center ofthellower end of the U.

Two substantially identical dish-shaped header plates 2 and 54 are then provided. These two plates are identical excepting that one of them, 44, is provided'with the previously referred to anged opening 26 at the center thereof. with the exception of the opening 26, only one,\42, needs to be described. It is formed of sheet metal which may have the same gauge as that-used for the tubes 14 and 16, but this is a matter where wide discretion Amay be eX- erciscd. The header plate42 is formed by drawing a metal blank so as to forma shallow dish having ailat surface completely surrounded by an upstanding flange 45. The contour of the end plate 42 is such thatit will nest within the generally U-shaped structure formed by the welded together tubes 14 and 16. At the top of the U, the bight 34 of the tube 14 is spaced from the similar bight 46 of the tube 16 by an appreciable distance and at this location the end plate 42 is formed to provide an upward extension 4S which forms shallowshoulders 5t? and 52 against which the most nearly adjacent portions of the bights 34 and 36 nest. With the plate 42 at one end nested between the tubes 14 and 16,` and with the similar plate de similarly nested at the opposite end thereof, the end plates are joined to the tubes by seam welding the tianges to the inner surface forming portion 32 of the tube 1.4 and the similar portion 33 of the tube 16.

Two additional shallow closure members are indicated in Fig. 3 at 54 and 56. These two closures are reverse complements of each other and are duplicated at the op- L posite end of the heat exchanger. The closure member -54- is roughly triangular in contour and has a continuous upstanding circumscribing flange generally similar to the flanged/t of the end closure member 42. At its upper edge the flange portion indicated at 58 is straight and horizontal and has a length just slightly greater than the similar hat lower surface of the tubes land 16, that is, the at surface 3S of the tube 14 and the similar counterpart 37 of the tube 16. At the right hand end of the yhorizontal flange portion 5S as seenl in Fig. 3, this flange is joined to a straight downwardly extending portion indicated at 6?. The lower end of this in turn is connected to a portion 62 which extends abruptly to the right and thence downwardly again for a short distance. The left hand end of the horizontal iiange portion 53 and the lower end of the portion 62 are connected by a generally convex tiange portion 64.

The external contour of these flange portions is such that when the flat surface 5S is nested'against the lower hat surface 37 of the tube 16 with the downwardly extending portion against the tab 40, the portion 62 which extends abruptly to the right will come into a positionl along the center line of the structure comprised of the tubes 14 and 16. in other words, the portion 62 is offset from the portion 60 to the right by an amount equal to approximately the thickness of the tab 40, or,

in other words, twice the thickness of the metal from `which the tube 16 is formed.

As vinthe previous instances, the four end closures 154 -and 56.and their counterpartsat the opposite-end ofthe Since these two members are identical heater,.arejoi.nedto..the, tubes A14 ,and .16 .by .seam welding or related resistance welding technique. The structure thus formed has generally smoothly convexly curved sides and a smoothly curved bottom which is slightly offset downwardly from the generally curved contour established by the two sides .o'f;.the tubes 14 and 16. At the top..the.structure.has..a .broadly rounded notch which extends `downwardly slightly and is formed by the juncture of the top surfaces of the'bights 34 and 46 of the tu'bcsait and .1&6 and they top angezportion 48 of the end central closure member-42.

rifhe outside enveloping sheet indicated generally at 10 is shown-as beingformedof a length of seamless tubing. lf desired, of course, this tube can be formed from a flat sheet rolled generally .to cylindrical contour with the edges seam welded together in overlapping relationship. in any event, the intermediate diameter of thc generally/.cylindrical enclosurefonned .by thezsheet 10 is larger than the'structure--whichis comprised'of thertubcs 2.4 .and 16,:.the `end closure members 42, .54 and-.56 and their counterparts at the .opposite end of ,the Lheat .exchanger. .This provides clearance between the'outcr shell and the tubes 14'and 16.

The two ends ofthe enveloping sheet 10 are so formed that the lower portions thereof generally maintain their original cylindrical contour. At least this portion tof .the shell is .curved in only Aone plane and tits againstthc flange 64 ofthe small ,endclosure member54 `and 'its counterpart on ,the adjacent yend closurefmember 56, and tiose Aat the opposite end of the heat exchanger. Upwardly of the ends of these tiange portions'the metalof the shell 1t) is bent inwardly and-shaped to conform '.to the exterior surfaces of the tubes 14 and 16 and to thc contour of the upper flange portion 48 .ofthe large closure member .42 and its counterpart at the opposite end of the heat exchanger.

In this connection it'should be vappreciated that :the intermediate diameter of the shell is considerablygreater than the largesttransverse dimension of the assembly'of tubes and end plates. It would appear therefore'that reducing the size of the ends of the shell to t the tube assembly would result in wrinkles in the shell material. This is compensated for, however, by the downward broad notch at the top of the tube assembly and the smaller notches at the outward ends of the end plates Stand S6. Stated differently, the circumference of the shell is about the same as the irregular linear dimension around the .end of the inner assembly. These dimensions can be adjusted to be the same,for instance by increasing or decreasing the amount of upward offset of the upward extension 43 on the centralend plate42 and 44. If with a particular design the shell is' too loose, the height of the extension 43 can be reduced so that the shell is made tighter by drawing it farther downwardly between the tops of the tubes 14 -and 16. The converse is of course also true.

After the shell 10 has been formed at both ends to the contour described, the tube and end closure assembly is slid endwise thereinto and seam welding or similar resistance welding techniques are used for joining the ends of the shell to the ends of the tube assembly completely around their peripheries in so far as this is feasible by using resistance welding techniques.

After the completion of this welding operationthe small voidsor holes indicated at 70, 72, 74, 76, 78, and 82, are filled by torch or vare welding. The similar voids at the opposite end of the heatexchanger are similarly filled.

The tubular exhaust fitting 12 is resistance welded to a anged opening 86 formed-at the bottom of the shell 10 and this operationof joining the spud 12 to the heat exchanger shell 10'may be conducted whenever convenient vduringy the fabricating process. That is for instance it may be performed as the last operation, or as the last operation before torch or arc welding, or it may be performed 4before theassemblyf-of thetubes 14-and l16and the end closure members attached thereto are slid into place in the vshell 10.

Referring now to Fig. 5, it will be seen that hot gases issuing from the burner which extends into the heater through the opening 26 can fill the central `space and flow upwardly as indicated by the arrows, around the tops of the tubes 14 and 16 and thence downwardly between these tubes and the outer shell so that these combustion gases come together in the longitudinally extending space beneath the flat surfaces `37' and 38. The combustion gases then ilow longitudinally as necessary so as to reach and pass through the exhaust Spud 12. The tubes 14 and 16 and the shell 10 are therefore efficiently heated and this heat is exchanged to the Ventilating air which passes longitudinally through these tubes and along the surface of the shell.

From the above it will be seen that a heater heat exchanger constructed according to the teachings of the present invention may be readily fashioned by relatively simple individual operations, and by comparatively simple production tools. Note also that although the welding operations require joining sheet metal members together over a considerable total linear distance, almost all of this can Ibe accomplished by efficient and low cost resistance welding technique. Although some final torch or arc welding is necessary to seal small holes, this operation can be quickly conducted and the Welding skill required is not high, particularly since the weld points are small as compared with the mass of metal surrounding them. Under these conditions little diculty is encountered in obtaining good welds since there is little danger of melting excessive amounts of the metal of the sheet metal members.

From the above description of a preferred embodiment of my invention it will be apparent that changes and substitutions can be made without departing from the scope or spirit of the invention and that therefore the invention is to be measured by the scope of the following claims.

Having described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. A heater combustion chamber and heat exchanger assembly comprising a pair of transversely flattened and curved longitudinally extending sheet tubes, each of said tubes being formed of a strip of sheet metal folded upon itself with its edges joined together in face to face relation by resistance welds to form a longitudinally extending tab outstanding from the main portion of said tube, the tabs of said pair being joined together in face to face relation by resistance welds so that said pair of tubes in cross section forms a generally U-shaped structure with a stiffening rib outstanding from the center thereof with the concave sides of said tubes facing each other to define a longitudinally extending central space between them, said space being open at the top through a longitudinally extending slot between the top edges of said tubes, a generally'cylindrical sheet metal tubular shell enclosing said U-shaped structure and spaced from said U- shaped structure intermediate the ends thereof, a pair of flanged enclosure members formed to fit the ends of the central space between said tubes, additional flanged end closure members formed to tit the ends of the spaces at each side of said rib, said shell being shaped inwardly at its ends to embrace the ends of said U-shaped structure and the flanges of said end closure members, said shell, said U- shaped structure, and said anges being secured together principally by resistance welds, one of said pair of end closure members being formed to provide a burner opening and means forming an exhaust fitting connected through `said shell at a position adjacent said rib.

2. A heater combustion chamber and heat exchanger assembly comprising a pair of transversely flattened and curved longitudinally extending sheet metal tubes, each of said tubes-being formed of a strip of sheet metal folded upon itself with its edges joined together in face to face relation `by resistance welds to form a longitudinally extending tab outstanding from the main portion of said tube, the tabs of said pair being joined together in face to face relation by resistance welds so that said pair of tubes in cross section forms a generally U-shaped structure with a stiffening rib outstanding from the center thereof with the concave sides of said tubes facing each other to define a longitudinally extending central space between them, said space being open at the top through a longitudinally extending slot between the top edges of said tubes, a generally cylindrical sheet metal tubular shell enclosing said U-shaped ystructure and spaced from said U-shaped structure intermediate the ends thereof, a

pair of anged end closure members formed to iit the ends of the central space between said tubes, additional ilanged end closure members formed to lit the ends of the spaces at each side of said rib, said shell being shaped inwardly at its ends to embrace the ends of said U- shaped structure and the anges of said end closure members, said shell, said U-shaped structure, and said flanges being secured together principally by resistance welds, the circumference of said shell being substantially the same as the peripheral distance around said tubes and end closure members, one of said pair of end closure members being formed to provide a burner opening and means forming an exhaust fitting connected through said shell at a position adjacent said rib.

References Cited in the le of this patent UNITED STATES PATENTS 135,422 Fridley Feb. 4, 1873 690,115 May Dec. 31, 1901 2,507,081 Allen et al. May 9, 1950 2,581,942 Collins et al. Jan. 8, 1952 2,725,930 Hillery et a1. Dec. 6, 1955 

